Styrenic resins such as HIPS (high-impact polystyrene) and ABS (acrylonitrile-butadiene-styrene) have excellent moldability, dimensional stability, impact resistance, and rigidity and therefore are widely used as constituent materials such as electric device parts, automotive parts, and building materials. The styrenic resins are required to have flame retardancy depending on applications thereof.
Most of materials meeting U.S. UL Standard 94 V-2 are required to drip as immediately as possible after being ignited for the purpose of ensuring higher safety since a burnt portion drips from a molded article to reduce a flame of the burnt portion or to extinguish a fire. That is, most of materials are required to have excellent dripping performance.
There is a conventional technique for blending a styrenic resin with a halogen-containing compound, such as a decabromodiphenyl ester, serving as a flame retardant and an antimony compound serving as flame retardant aid for the purpose of imparting flame retardancy to the styrenic resin. However, the halogen-containing compound decomposes during burning to generate gases harmful to human health and therefore has environmental problems.
Therefore, techniques using a non-halogenated flame retardant have been proposed as described below.
For example, Japanese Patent Publication 57-1547 A proposes a technique for blending a styrenic resin with a composite metal hydroxide. However, the composite metal hydroxide is less effective in improving flame retardancy though a large amount of the composite metal hydroxide is blended, as is clear from Examples described therein.
Japanese Patent Publication 10-130454 A proposes a technique for blending melamine isocyanurate and/or melamine polyphosphate. This technique requires the use of a phosphoric ester which causes reductions in mechanical properties and heat resistance of an article.
Japanese Patent Publication 10-120853 A proposes a technique using a phosphoric flame retardant such as a phosphoric ester.
It is known that phosphoric flame retardants such as phosphoric esters form carbonized layers during burning to provide flame retardancy. It has been considered that the larger the content of phosphorus in a material is, the higher the effect of imparting flame retardancy is.
However, the phosphoric flame retardant acts as a plasticizer for resins. Therefore, there is a problem in that reductions in mechanical properties and heat resistance are caused although flame retardancy is enhanced by the blending of the phosphoric flame retardant.